Such an adjustable front sight for a gun in the M16 series is already known. The front sight is constituted by a part provided with an end constituting the sight proper and with a threaded body screwed into a tapped hole in the top cross-member of the front sight support, between the two side plates. The front sight also includes an intermediate part in the form of a washer with peripheral notches, e.g. four notches. A locking stud is provided on the circle of the peripheral notches, sliding in a hole and bearing against the bottom thereof by means of a spring. The locking slide is formed of a cylindrical body terminated by an end that is also cylindrical, but of smaller diameter so as to form a shoulder.
This smaller end occupies a corresponding notch of the front sight disk, while bearing against the bottom face of the disk via its shoulder.
To adjust the front sight, i.e. to lower it by screwing it in or to raise it, it is possible to use a hook or a point to press down the member that prevents rotation so as to retract it, thereby allowing the front sight to be turned using a special tool in the form of a tube provided with teeth that engage in the notches of the front sight disk. The tooth overlying the locking member pushes away said and allows the front sight to be turned since the other teeth are occupying the other notohes in the front sight disc, thereby preventing the looking member from moving beak out.
Nevertheless, this operation is relatively fiddly since the locking member will move back out whenever the next notch come over the housing for the locking member.
That front sight therefore suffers from the drawback of requiring special tool which is relatively small and easily lost, or which is not easy to handle in order to perform adjustment.